Currently I have a Windows 2000 machine accepting dial-in ppp connections. And i hear It is possible to have OpenBSD do that. but I cant find a good tutorial on the Net of how to do this. Does any body know of one or could write instructions of how to do this. Either would be greatly appreciated.

Currently I have a Windows 2000 machine accepting dial-in ppp connections.

If this modem is part of the motherboard, be forewarned that it may be a Winmodem -- meaning that it is not a complete hardware implementation of a modem, but expects a software interface to emulate part of hardware. You will find this as unlisted in the hardware compatibility list:

Does any body know of one or could write instructions of how to do this.

The *BSD world, & especially the OpenBSD community, frowns on tutorial information found in the wild as it is frequently old, out-of-date, incomplete, or simply incorrect. The best place for tutorial information is the FAQ itself. Section 6.5 of the FAQ covers userland PPP configuration. Start here. If you are game for configuring the kernel pppd(8) daemon, start with Section 6.5 followed by studying the manpages.